This essay is adapted from “Sex After …: Women Share How Intimacy Changes as Life Changes,” by Iris Krasnow, published by Gotham Books

WASHINGTON — I have spent the last two years digging into the sex lives of some 150 women, ages 20 through 90, for my new book “Sex After … Women Share How Intimacy Changes As Life Changes.” I talked to women at all phases of their lives, in college, newly married, going through menopause, and in widowhood. What surprised me the most were the voices in the “Giddy Golden Girls” chapter. Those women revealed how sex at their age with the right partner can be the best sex they have ever experienced.

A 77-year-old told me she was inspired to try fellatio for the first time after watching a YouTube video titled “Learn How to Give a Blow Job Like a Pro.” She practiced on a banana, which is the advice of Dr. Ruth Westheimer, the intrepid 85-year-old sex therapist whom I also interviewed for the book. Dr. Ruth now has her own YouTube channel. Westheimer told me that women in their 70s and 80s are some of her most active advice-seekers, and that they are curious about masturbation, vibrators and oral sex.

My first conversation took place at a bookstore in San Diego. I was flipping through a copy of “Lady Chatterley’s Lover,” refreshing my memory of that iconic work of erotica, when a silver-haired saleswoman told me I should also buy “Fifty Shades of Grey.” “I am 75, and it was my older sister who recommended them,” she added. “My sister said some of the scenes gave her more orgasms than she’d had since her 30s. You do know that old people do it, too.”

Now, after many more interviews, I know it very well. Standing barely 5-feet tall, 88-year-old Libby spoke of her colossal sexual appetite up until her husband’s death, at the age of 91. “We were married for 58 years and to the end of his life, George and I never lost the magic of our physical attraction for each other,” Libby said. “This business that every woman over the age of 70 or 80 doesn’t lubricate is nonsense. I guess people today would call us sex addicts, because we made love so often and thought about it every day. We would spend hours in bed, and we would talk and laugh and roll around. To maintain a long physical attraction the relationship also has to be a mental and emotional connection.”

I was giving a talk at a clubhouse of a West Coast oceanfront community on the topic of sustaining romance in marriage. In her orange pantsuit and lipstick to match, Shirley sparkled in the crowd of 100 senior women. After my talk, she leaned over and whispered (I could smell her Shalimar): “Call me. I’m 72 and I am having the best sex I’ve ever had in my life.” I did call her, and Shirley revealed secrets that made me feel like taking an ice bath.

“Every week we put a date and a time on our calendar to make love,” Shirley began. “On that day, I put on a gorgeous, sexy nightgown and that makes it even more exciting. We also find that a little bit of marijuana is a nice addition to our sex lives. I am having some of the hottest sex now, better than I had in my 20s or 30s or 40s. One of my secrets is that we are so comfortable with each other that we will try anything to keep things hot.”

“We’ve also incorporated some very inventive sex toys into our sessions, and that combination of feeling wild abandon and total comfort has been just amazing,” Shirley continued. “After 70, there comes a sweetness about making love. We go slowly, there is no rush anymore. When you’re younger, it’s all about the orgasm, then it’s over. I love this suspended feeling, the absolute intimacy we have been able to achieve.”

That I found septuagenarians like Shirley not to be rare creatures is emblematic of these times of elongated fitness and life spans — and hormone therapies — when women can flex and explore their sexuality way past midlife. “I get about two women a month asking me, ‘I’ve never used a vibrator; am I too old for one?,’ ” said sex therapist Ginger Manley, an associate in psychiatry at Vanderbilt University. “One woman in her early 80s came to me. Her husband had died and the issue with them was that she hadn’t been able to have an orgasm. She said, ‘I don’t want to die without having an orgasm.’ She got herself a good vibrator and that was that.”

Another woman I spoke to, Dorothy, got herself a lover and that was that. The only man she had ever slept with was her husband of 55 years, an Alzheimer’s patient she had cared for during his decade-long demise. He died a year ago, but their sex life had died long before that. Standing graveside, exhausted and depressed, Dorothy was certain she would never be in someone’s arms again. A chance meeting with a childhood friend she had not seen for more than 50 years changed that dark forecast.

“The two of us grew up in the same neighborhood. We were never boyfriend and girlfriend, just friends,” said Dorothy. “Then we run into each other at a funeral after no contact for 54 years. We gave each other a hug and it was electric, a shock went through my entire body. It was amazing. It was like magic. He called me the next day and we set up a lunch date, and we both knew there was a powerful connection. When he took me home all of a sudden he said, “You want to go into the bedroom?” This was our first date! Well, we stayed in bed for five hours. We had sex, then we took a little nap, then we had sex again. And we talked and we talked, and then he would say, ‘we’re not done yet’ I said, ‘Listen we’ve got to stop. I’m not used to this.’ And this has been going on for six months now.”

In my many years writing books about intimate relationships one of my favorite go-to experts is Dr. Marilyn Charwat. She is a 79-year-old, sexily married sex therapist in Boca Raton, Fla., hometown to many women in her age range dating after widowhood, or hungry for tips on how to heat up stale, old marriages. With long black Cher hair and a yoga-toned frame, Charwat is ageless and unfailingly provocative.

“I am a big believer in women having orgasms once a day, or at least three times a week. Because an orgasm, like a Kegel, lifts and tightens the pelvis. An orgasm provides tremendous relaxation and it also helps keep the vagina healthy and lubricated. If you get used to having regular orgasms that whole part of your body is being revitalized, your whole life is revitalized. Also, if you learn to bring yourself to orgasm, you can have more fulfilling sex with a partner because you know what you need.”

“Happily, I can report there is a lot of sex going on with people my age, and older. Because most people in their 70s and 80s feel internally like they did when they were 35. When it comes to enjoying a long and healthy sex life, attitude is everything.”